An outer case of an electronic device including therein an acoustic unit such as a speaker unit has a sound hole through which the acoustic unit emits or collects sound. The outer case includes therein various electrical circuits or the like, and thus needs to block entry of moisture through the sound hole to protect the electrical circuits or the like. A conventional proposal for a waterproof structure for blocking entry of moisture into such an outer case to protect electronic components has been known (see Japanese Laid-open Patent Publication No. 07-131375).
FIG. 8 illustrates a conventional waterproof structure for blocking entry of moisture into an electronic device 100. FIG. 8 illustrates the waterproof structure in section.
An outer case 101 of the electronic device 100 has a sound hole 102. The outer case 101 includes therein an acoustic unit 103 in a position corresponding to a position of the sound hole 102. Also, a sheet member 104 is provided between the outer case 101 and the acoustic unit 103. The sheet member 104 is a water repellent sheet. The sheet member 104 blocks entry of moisture into the outer case 101 through the sound hole 102.
A mounting portion 105 mounted to the outer case 101 is circumferentially provided on an outer peripheral portion of the sheet member 104. The mounting portion 105 is formed by bonding a cushion material or a rigid material to the outer peripheral portion of the sheet member 104. The mounting portion 105 is mounted in tight contact with an inner surface of the outer case 101. The acoustic unit 103 is mounted to the mounting portion 105. A double-faced tape 106 is provided as a buffer between the mounting portion 105 and the acoustic unit 103. The double-faced tape 106 increases sealability around the acoustic unit 103 and prevents sound leakage from the acoustic unit 103. The double-faced tape 106 is placed on an outer periphery of the acoustic unit 103 so as not to close a sound emitting portion 103a having a hole for emitting or collecting sound. A cushion material may replace the double-faced tape 106.
The sheet member 104 blocks entry of moisture into the outer case 101, and also attenuates sound emitted or collected by the acoustic unit 103. Thus, the sheet member 104 needs to have a minimum area required for maintaining desired acoustic characteristics of the electronic device 100. The minimum area required for the sheet member 104 is an area corresponding to acoustic characteristics such as sound pressure of the acoustic unit 103.
Meanwhile, acoustic units have been reducing in size corresponding to an increasing need for a reduction in size of electronic devices. Recent small-sized acoustic units have been able to exhibit acoustic characteristics such as sound pressure equal to those of conventional acoustic units.
However, if a small-sized acoustic unit that can exhibit the same acoustic characteristics as a conventional unit is mounted in an electronic device, the following problems occur in terms of the need for the sheet member 104. The problems will be described with reference to FIG. 9. FIG. 9 illustrates in section a state where the outer case 101 includes therein an acoustic unit 203 having a smaller size than the acoustic unit 103 in FIG. 8 instead of the acoustic unit 103. The acoustic unit 203 has acoustic characteristics equal to those of the acoustic unit 103.
When the small-sized acoustic unit 203 is used, a sheet member 104 needs to have an area equal to that of the conventional acoustic unit. Thus, the same sheet member 104 as illustrated in FIG. 8 is used. A mounting portion 105 is circumferentially provided on an outer peripheral portion of the sheet member 104, and this is the same as in FIG. 8.
When the same sheet member 104 is used conventionally, the small-sized acoustic unit 203 may be located inside the circumferentially provided mounting portion 105. In such a state, the acoustic unit 203 cannot be mounted to the mounting portion 105. Specifically, a double-faced tape 106 provided on an outer periphery of the mounting portion 105, so as not to close a hole 203a of the acoustic unit 203 for emitting or collecting, sound comes into direct contact with the sheet member 104. This may cause break or failure of the sheet member 104. The breakage or failure of the sheet member 104 prevents an appropriate waterproof effect from being maintained.